feat: distinguish Freighter locked state from not-installed with clear UI

[Horlarmmy]

Summary

Closes #809

When Freighter is installed but locked (password-protected), the wallet connection flow previously showed the same "Install Freighter" modal as when the extension is not installed at all. This led to confusing guidance — users were told to install something they already had.

This PR detects the locked-wallet error distinctly and surfaces copy telling the user to unlock Freighter rather than reinstall it.

Changes

src/utils/freighterErrors.ts

• Added FreighterLockedError class
• Added isFreighterLockedError(error) — detects error messages matching patterns like "freighter is locked", "wallet is locked", "unlock your wallet", "extension is locked"

src/components/InstallFreighterModal.tsx

• Added optional isLocked prop (default false)
• When locked:
  • Heading: "Freighter Wallet Locked" (vs "Freighter Wallet Required")
  • Body: instructs user to unlock Freighter with their password
  • Amber info box replaces the "Install Freighter" CTA link
  • Retry button: "I unlocked it — check again"

src/components/WalletContext.tsx

• Added isFreighterLocked state
• After getAddress() returns, checks key.error for locked patterns (Freighter API v6 returns error objects, not thrown exceptions)
• Also checks the catch block for thrown locked errors
• When locked: shows the modal with isLocked=true instead of the generic error toast
• handleRetryInstall simplified — closes modal, resets locked flag, calls connectWallet() which re-opens in the correct mode if still locked

src/components/__tests__/WalletContext.test.tsx

• Added "connectWallet - freighter locked" test — mocks getAddress to return { error: { message: "Freighter is locked" } }, verifies locked-specific heading and unlock guidance appear

Flow

Scenario	Before	After
Not installed	Modal: "Freighter Wallet Required" + Install link	Same (unchanged)
Installed & locked	Modal: "Freighter Wallet Required" + Install link	Modal: "Freighter Wallet Locked" + unlock guidance
Installed & unlocked	Connection succeeds	Same (unchanged)

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[sshdopey]

Auto-review failed (API error). Leaving PR for human review.